Color printers in which primary-color images are accumulated on a photoreceptor and transferred to an output sheet as a full-color image are known.
Color printers commonly have a control system including monitors which can make measurements of images created on the photoreceptor or of images which were transferred to an output sheet. These monitors are typically in the form of optical densitometers. The information gathered therefrom is used by the control system to modify printer outputs to the photoreceptor or output sheet in various ways to aid in the operation of the printer. These effects can occur in a real-time feedback loop, an offline calibration process or a registration system.
Typically, a printer using a control system which relies on a monitor requires the deliberate creation of what shall be herein called “test patches”. Test patches are made and subsequently measured in various ways by the monitors. These test patches are images of a desired darkness value, a desired color blend, and/or a particular shape, such as a line pattern; or they may be of a shape particularly useful for determining registration of superimposed images (“fiducial” or “registration” marks).
Conventional densitometers are limited in the amount of information they can generate due, in part, to limitations in the space over which they gather information and limitation in the portion of the spectrum over which the information is gathered.